Submerged vehicles, such as unmanned underwater vehicles (UUVs), are used in a variety of military applications, for example, surveillance, reconnaissance, navigation, and defense. When these vehicles are submerged, however, navigation and communication are difficult. Inertial navigation systems, such as gyroscopes or other computer and motion sensors that track position, orientation and velocity can be used, but these systems are subject to drift the longer they remain below the water surface. Highly accurate global positioning system (GPS) navigation systems and high-bandwidth radio frequency (RF) communications links are not directly available to submerged vehicles due to the rapid attenuation of radio frequency energy by water. Thus, submerged vehicles are limited to communicating with low bandwidth acoustics or wiring back to another vessel or shore platform.
Prior art communications devices for submerged vehicles, such as the device disclosed in U.S. Pat. No. 5,379,034, rely primarily on buoyancy to float an antenna to the water surface. The tow angle β of a tethered cable, calculated as the angle between the cable and the direction the submerged vehicle is traveling, is affected by the speed of the submerged vehicle. The faster the vehicle travels, the smaller the tow angle β, resulting in the tethered cable being pulled straight back and the communications device never reaching the water surface. The slower the submerged vehicle travels, the larger the tow angle β, resulting in the tethered cable drifting straight up and the communications device drifting to the surface. Prior art devices that rely primarily on buoyancy require the submerged vehicle to be stationary or to be traveling at significantly reduced speed in order for the antenna to drift to the surface. Thus, submerged vehicles using these prior art devices cannot simultaneously communicate and travel at operational speed. Other prior art systems, such as those disclosed in U.S. Pat. Nos. 3,972,046 and 7,448,339, rely on an intermediary float tethered to an underwater vehicle and a surface float having an antenna. These prior art systems operate at very limited speed ranges because the surface floats would be pulled underwater at all but the slowest speeds. Additionally, the intermediary floats of these prior art systems are towed underwater, thereby increasing the probability of entanglement and drag when deployed. Still other prior art arrangements, including the antenna arrangement disclosed in U.S. Pat. No. 6,058,874, do not provide for conformal stowage in which a tethered communications device can be stowed within and be quickly deployed from an underwater vehicle, thereby, minimizing drag and the likelihood of vehicle entanglement during operation.
Accordingly, there is a need and desire for an efficiently deployable tethered communications apparatus and system for providing submerged vehicles with bi-directional, high data rate communications to a nearby vessel or shore platform as well as GPS coordinate data for precise navigation while traveling at operational speed.